1. Field of the Invention
The present invention relates to a heater to be effectively used in the fixing device of an image forming apparatus, such as a copying machine or a printer, and to an image heating apparatus equipped with this heater.
2. Related Background Art
Conventionally, a heating apparatus (fixing device) using a heat roller fixing system is well known as a heating apparatus for use in an electrophotographic image forming apparatus, such as a copying machine or a laser beam printer.
However, in this system, it is necessary to always maintain high temperature, resulting in large energy consumption, which is contradictory to energy saving. Further, heat emission occurs in the apparatus even during standby, resulting in an increase in the temperature of the interior of the apparatus.
Further, it takes time to heat the roller up to a temperature suitable for heating an object to be heated, such as a paper sheet.
In view of this, Japanese Patent Application Laid-Open No. 63-313182 proposes a method according to which a resistive heat body pattern is provided on an insulating ceramic substrate to form a heater, which is caused to dissipate heat to thereby heat the object to be heated through a thin film.
In this method, the temperature of the heating body rises in a short time, so that if the object to be heated is fed without being warmed up, it is possible to heat up the heater to the desired temperature before the object to be heated in the form of a paper sheet has reached the fixing nip. Further, since no heating is effected during standby, there is no temperature rise in the apparatus, nor is there any energy consumption.
Further, in this film heating fixing type heating apparatus (fixing device), to charge the film surface with a charge of a predetermined polarity, a bias is applied to the film, and a conductive ring which is in contact with an end portion of the film is provided in an end portion of a pressure roller opposed to the heating body with the film therebetween, the bias being applied to the film through the conductive ring.
However, in the film heating fixing system described above, for example, a heating body is in contact with the conductive ring at an end portion of the heating body, so that heat is easily taken away from the end portion of the heating body through the conductive ring, with the result that the quantity of heat imparted to the object to be heated is uneven inside the nip.
Further, when, for example, the factor taking heat away at one end differs from that at the other end in the longitudinal direction, the temperature of the end portion from which more heat is taken away becomes lower than that of the other portion.
This phenomenon adversely affects the image quality when forming an image since it leads to faulty end-portion fixing, uneven fixing, and uneven glossy.
Such a problem occurs not so often when the heat conductivity of the substrate of the heating body is 10 to 30 [W/mxc2x7k]. However, when a material whose heat conductivity is higher than that, ranging, for example, from 50 to 150 [W/mxc2x7k], is used as the heater substrate, the above problem is particularly likely to occur.
The present invention has been made in view of the above problems inherent in the prior art. It is accordingly an object of the present invention to provide a heater capable of suppressing faulty image heating, and an image heating apparatus equipped with this heater.
Another object of the present invention is to provide a heater capable of evenly heating an image borne by a recording material, and an image heating apparatus equipped with this heater.
Still another object of the present invention is to provide an image heating apparatus comprising:
a heater for heating an image on a recording material, the heater having a heat dissipation resistor; and
a backup member for forming a nip cooperating with the heater,
wherein the heat dissipation amount per unit length of the heat dissipation resistor differs between a middle zone and first and second edge zones, and wherein the heat dissipation amount per unit length of said heat dissipation resistor also differs between the first edge zone and the second edge zone.
A further object of the present invention is to provide a heater comprising:
a substrate; and
a heat dissipation resistor formed on the substrate,
wherein the heat dissipation amount per unit length of the heat dissipation resistor differs between a middle zone and first and second edge zones, and wherein the heat dissipation amount per unit length of said heat dissipation resistor also differs between the first edge zone and the second edge zone.
A further object of the present invention is to provide an image heating apparatus comprising:
a heater for heating an image on a recording material, the heater having a heat dissipation resistor; and
a backup member for forming a nip cooperating with the heater,
wherein the heat dissipation resistor has a uniform heat dissipation amount per unit length in the longitudinal direction, and is divided into a left zone and a right zone differing in length with respect to a conveyance reference for the recording material.
A further object of the present invention is to provide a heater comprising:
a substrate; and
a heat dissipation resistor formed on said substrate,
wherein said heat dissipation resistor has a uniform heat dissipation amount per unit length in the longitudinal direction, and is divided into a left zone and a right zone differing in length with respect to a conveyance reference for a recording material.
A further object of the present invention is to provide an image heating apparatus comprising:
a heater for heating an image on a recording material, the heater having a heat dissipation resistor; and
a backup member for forming a nip cooperating with the heater,
wherein the heat dissipation amount per unit length of said heat dissipation resistor differs between a middle zone and first and second edge zones, and wherein the first edge zone and the second edge zone differ in length.
A further object of the present invention is to provide a heater comprising:
a substrate; and
a heat dissipation resistor formed on the substrate,
wherein the heat dissipation amount per unit length of the heat dissipation resistor differs between a middle zone and first and second edge zones, and wherein the first edge zone and the second edge zone differ in length.
A further object of the present invention is to provide an image heating apparatus comprising:
a heater for heating an image on a recording material, the heater having a heat dissipation resistor;
a supporting member for supporting the heater; and
a backup member for forming a nip cooperating with the heater,
wherein the supporting member has a heat insulating means at a position corresponding to at least one of first and second edge zones of said heat dissipation resistor.
Further objects of the present invention will become apparent from the following detailed description made with reference to the accompanying drawings.